NITROGENATION OF R2FE17 COMPOUNDS - R = RARE-EARTH

The reaction between nitrogen gas and the series of R2Fe17 intermetallic compounds is studied by thermopiezic analysis on micron-size powders. Nitrogen diffusion in the range 300-550-degrees-C can be represented by an activated interstitial diffusion process D = D0e-E(m)/kT with D0 = 1.95 X 10(-10) m2s-1 and an activation energy E(m) = 0.81 eV. This stage of the nitrogenation reaction leads to the formation of R2Fe17N3-delta nitrides which have structures related to those of the parent compounds. Heating above about 800-degrees-C leads to complete disproportionation of the compounds into a mixture of rare-earth nitride and iron.